5.V=π×r×r×h 6.28÷0.4=157棵=3.14×（40÷2）×（40÷2）×50=62800立方米=6.28升6.(1)3.14×2×2+3.14×2×2×15=106.76立方米（2）半个圆柱的体积=π×r×r×h ÷2=3.14×2×2×15÷2=94.2立方米7.圆锥的体积...